Caption: Cutaway drawing of Franchot's Moderator pressurised oil lamp patented in 1836 by the French inventor and mechanic Charles-Louis Franchot (1809-1881) from Carcel's more complicated lamp of 1800. Vegetable oil such as colza, carcel or rape-seed gave a clear, smokeless, odourless flame, but was too heavy to move easily to the lamp's wick and tended to clog the burner. It was also relatively expensive. Forcing oil to the burner, rather than relying on capillary action, produced a superior flame. Franchot's moderator lamp employed a clockwork-driven spiral spring-operated piston to pressure-feed the burner through a constricting valve (the moderator) which ensured constant fuel pressure. However, though the mechanism was fairly difficult to maintain and required frequent winding, it was widely used and provided the light source in lighthouses.